You obviously are aware of your central health problem, which isn't HIV or your sexual behavior. I can do nothing more than tell you that the chance of HIV infection from the exposure you describe, shaving or not, sexual position or not, vaginal secretions getting into shaved area or not, is close to zero.
I can offer only 2 suggestons. First, call your partner and ask if she is HIV infected; she probably isn't (and will probably tell you the truth). Second, follow through with your mental health provider, which you undoubtedly realize you need to do anyway.
Good luck-- HHH, MD
Feel free to continue to post comments if you wish; you might get helpful information from other forum participants. But I'm not going to reply further.
HHH, MD